Reduction of disulfide bonds and introduction of "de novo" thiol groups in cyclodextrin glucantransferase from sp. were assessed in order to perform reversible covalent immobilization onto thiol-reactive supports (thiolsulfinate-agarose). Only the thiolation process dramatically improved the immobilization yield, from 0 % for the native and reduced enzyme, up to nearly 90 % for the thiolated enzyme. The mild conditions of the immobilization process (pH 6.8-7.0 and 22 A degrees C) allowed the achievement of 100 % coupling efficiencies when low loads were applied. Ionic strength was a critical parameter for the immobilization process; for high activity recoveries, 50 mM phosphate buffer supplemented with 0.15 M NaCl was required. The kinetic parameters, pH and thermal stabilities for the immobilized biocatalyst were similar to those for the native enzyme. For beta-cyclization activity, optimal pH range and temperature were 4.0-5.4 and 85 A degrees C. The possibility of reusing the support was demonstrated by the reversibility of enzyme-support binding.